The invention relates to a method for manufacturing foamed products according to the preamble of claim 1. Such a method is known from International patent application WO 96/05254. The invention further relates to an apparatus that can be used therefor and to products that can be obtained according to this method.
The products to be manufactured according to the invention have a foamy structure. More particularly, the foamy material always comprises at least three parts: two relatively dense layers on the outside, which, as it were, form a skin, and between them a foam structure as core. The dense layers are firm and strong and consist of substantially closed, small cells. The foam structure of the core is generally open, which means that the cells have burst to allow the gasses evolving during the manufacture, for instance water vapour or carbon dioxide, to escape. The cells generally have a firm and solid cell wall due to the relatively high pressure and temperature during the process. In the manufactured product, the fibers extend between and possibly partly through the cells and are mainly intricately connected to the material of the cells.
In this description, xe2x80x9cgelatinizationxe2x80x9d is understood to mean a change of a natural polymer from a slightly or completely loose granular or comparable granulate form into a cohesive form which may or may not be dry and/or foamed, in which stretched polymers are present. That is to say, a transition occurs from a solid substance, a colloidal solution or suspension to a more homogenous fluid mass. Depending on the polymers used, xe2x80x9cgelatinizationxe2x80x9d should therefore be understood to include, for instance, gelling, gellating and the like.
In foamed products where only gelatinization occurs, as a result of gas evolution, bubbles are formed in the mass to be foamed, substantially after gelatinization. This process occurs at relatively lower temperatures and pressures. Over the entire cross section, such products have approximately the same structure of relatively small cells with walls of substantially uncross-linked natural polymers.
In this description, xe2x80x9cbakingxe2x80x9d is understood to mean a method in which both gelatinization and cross-linking occur, at relatively high temperatures and/or pressure. As a result, the formation of gas arises relatively soon, so that bubbles are already formed prior to or during gelatinization. As a result of inter alia the high pressure adjacent strongly heated parts, the polymers cross-link quickly when using a mould or like baking form with a temperature at or above the baking temperature.
These baked products have a core with relatively large cells, enclosed between skin parts with relatively small cells. The cell walls have a relatively high density and the natural polymers included therein are cross-linked to a high extent, which means that they have entered into mutual chain bonds. Such a baked product therefore has a sandwich-like structure.
In the method known from WO 96/05254 and WO 95/20628, an open platen set is employed, wherein products are manufactured from a batter comprising natural polymers, inorganic filler, water and fibers. The batter is introduced into the bottom half of an open platen set, for instance a baking iron, after which the platen set is closed and heated, so that the batter is gelantinized. The products obtained are thin-walled and biodegradable, which is advantageous from an environmental point of view. The fibers added have the advantage that an increase of the product strength is thereby obtained relative to products wherein such fibers have not been added. Such products are for instance known from WO91/12186.
A disadvantage of the use of platen sets is that the batter is introduced into an open mould which is subsequently closed and, for instance, is passed through a continuous oven, where it is heated, for instance by gas burners. Energetically speaking, this is little efficient and moreover the temperature in the baking mould is not properly controllable and may vary strongly during the baking process, which is not beneficial to the quality of the products. Moreover, the products which are obtained according to this method are not particularly dimensionally stable and allow no or only very slight differences in wall thickness, because otherwise no homogenous structure can be obtained. A further disadvantage of this method is that the introduction of the batter and the removal of the product is very laborious and will often lead to failure in the production. Moreover, with this method no products can be manufactured that are non-withdrawable, so that the freedom of design is limited.
In a further method according to WO 96/05254 a powderlike mixture of natural polymers, inorganic filler, water and fibers is introduced into a conventional EPS mould by use of an airstream through said mould. The mixture is heated inside the mould by use of heated steam, in order to provide for gelatinization and foaming of the mixture for forming the desired article.
In this method the mixture is introduced into the mould relatively slowly, which results in relatively long production times and can only be used with moulds having relatively easy designs and short flow paths. Furthermore, the products resulting from this method have to be stabilized by conditioning them, resulting in even longer production cycles.
European patent application 0 118 240 discloses a method for manufacturing biodegradable medicament capsules and like products by injection-moulding from a starch composite. To that end, a starch mixture with a low water content is introduced into a closed space, in particular the hopper of an injection-moulding machine, where plasticization of the mixture is provided for at a suitable specific temperature, pressure and humidity. The temperature and pressure are increased to such an extent that the mixture is adjusted to above the verification point. Thereafter the plasticized mixture is forced into a cooled mould and maintained under pressure, until the or each product has cooled off sufficiently, whereafter the mould is opened and emptied.
The advantage of this known method is that dimensionally stable biodegradable products can be manufactured relatively fast. However, the possible dimensions of products that can be manufactured with this method are limited, owing to the flow path in the mould. In fact, the plasticized mass forced into the mould is cooled directly, which gives rise to solidification and prevents flow of the mass relatively soon after entry of the mould. Moreover, no cross-linking of the starch in the mass occurs, so that the products have relatively weak strength properties and exhibit relatively poor resistance to water and moist conditions in general. In a moist environment the products will take up a great deal of water and thereby become slack; conversely, in a dry environment moisture will evaporate from the products, so that they become hard and brittle. The products obtained with this method have a high density and have no foamy structure.
International patent application 95/04104 discloses a method for manufacturing foamed, biodegradable products from starch-containing raw materials, in which an amount of a starch is liquefied in a pre-stage by heating to a temperature far above the gelatinization temperature, whereafter an amount of water-saturated ramie fibers is admixed. This mixture is thereafter passed into or through the mould or converted to a dry granulate. Upon heating of the mixture, the water is to escape from the ramie fibers and to function as blowing agent. When using this known method, a substantially dry granulate of starch is to be strongly heated in the pre-stage, which granulates therefore cannot form a liquid batter. This known method has the disadvantage that the raw materials are to be supplied in relatively dry form and in the pre-stage are to be mixed with the moist fibers under simultaneous increase of the temperature in the tank, whereby the desired gelatinization occurs. To that end, the mixture must be heated, which is difficult to effect homogenously in view of the relatively large mass. As a consequence, the process is relatively poorly controllable. A further disadvantage is that the products obtained in this way have only limited durability and are not water-resistant and moreover are not particularly dimensionally stable. With this method, the freedom of design is limited. Hence, this method suffers from the drawbacks mentioned in respect of the gelatinization of the mass prior to its introduction into the mould.
Further, European patent application 0 634 261 discloses a method for manufacturing biodegradable products utilizing a kind of injection-moulding technique, which starts from a mixture of a first and second biodegradable starting material. The first has a melting temperature of above 100xc2x0 C., the second of less than 100xc2x0 C. Either a substance which contains water is added to the starting material, or water is incorporated in the starting material, in such a manner that it can provide for the blowing of the cells. In an extruder press, the mass is heated to above the gelatinization temperature of at least the first starting material, mixed and pressurized and subsequently sprayed into a mould cavity provided in a pressurized space. After introduction of the mass, the pressure is removed, so that the water in the mass expands, blows the cells and exists through the permeable wall of the mould cavity. Such a method requires a complicated composition of starting materials. Further, this known apparatus has the above-mentioned disadvantages resulting from the gelatinization of at least a part of the mass prior to its introduction into the mould. In particular, as a result of inter alia the porous walls, the outer wall portions of the products manufactured according to this method will not have a dense, compact wall but a uniform distribution of cells of uniform size throughout the product thickness.
The object of the invention is to provide a method for manufacturing foamed products, in which the supply of the starting material is simple, in which the manufactured products are simple to remove from the mould, which involves a relatively great moulding freedom and whereby the manufactured products have a good dimensional stability and exhibit relatively good resistance to different conditions, including moist environments and temperature fluctuations, which products can moreover be integrated in a paper-reuse flow (paper recycling).
Owing to the supply of the mass from which the or each product is to be formed at a temperature which is below the gelatinization temperature, the supply of the mass can be realized in a simple manner, for instance via pumps and pipes. Moreover, a stock of the mass can be priorly prepared and be fed to a processing apparatus directly from a storage tank. By subsequently passing the mass under pressure into or through the mould and only heating it in the mould, it is ensured that the mould is always filled sufficiently. The flow path, that is, the or each path traversed by the mass to and in the mould can then be long to very long with respect to the cross sections of the passages. Only in the mould, the eventual gelatinization of the natural polymers occurs and then cross-linking of those polymers.
Due to the cross-linking that occurs, a firm product is obtained. The natural polymer provides for a relatively firm skeleton which extends around preferably continuous cells that form in the mould due to moisture or other blowing agents which, as a result of the heat in the mould, attempts to escape from the mass and due to the pressure in the mould, forms bubbles. As a result, the product obtained has a blown foamy structure. Since the natural polymer provides for a relatively stiff jacket, the thus obtained product is dimensionally stable upon exiting from the mould. Depending inter alia on the extent of cross-linkage, the product obtained is more or less flexible.
Since the mould is heated and not the mass prior to being forced into the mould, the temperatures in the mould can be properly controlled, both for the mould as a whole and for each separate portion thereof. As a result, products can be manufactured with different and verying wall thickness and with different mechanical properties. In fact, by heating more or less and/or for a longer or shorter period and adjusting, for instance, the pressure, for instance the extent of cross-linkage of the polymers can be controlled locally, so that the mechanical and physical properties are influenced. All this can be simply determined by those skilled in the art.
Heating the mass to the baking temperature, hence in excess of 100xc2x0 C., offers the advantage that the occurrence of fungoid growth is prevented, or at least substantially slowed down. The addition of fibers, in particular natural fibers, offers the advantage that the products are more dimensionally stable after injection moulding and heating, and remain shape-retaining, also in moist conditions. The products obtained with a method according to the invention are relatively strong and compression-resistant, impact-resistant and relatively elastic, insulating and can be reduced without involving fragmentation. After use, the products can be included in an existing waste flow for, for instance composting or, more advantageously, in a paper-recycling flow.
By utilizing natural fibers, in particular fibers of, for instance, annual plants and/or recycled fibers such as cellulose fibers from paper and wood waste, significant advantages are realized in terms of environment and manufacture. For instance, the emission of harmful substances is reduced, if not prevented, during manufacturing as well as during waste processing. As no fossile resources are used in the products, the processing thereof will cause no permanent increase of CO2 in the atmosphere, so that these products do not contribute to the so-called hothouse effect.
A further important advantage realized through the addition of fibers is that the obtained product retains its original shape and properties longer than it does without fibers. It is true that composing, i.e. the biological degrading process, proceeds relatively slowly, so that the product is less suitable for inclusion in a flow of vegetable, fruit and garden waste, but the product is thereby sufficiently durable for being able to serve as, for instance, packaging material, also if the articles packaged therein are stored and/or dispatched for a long time, or under unfavorable conditions, such as high temperature and/or high air humidity. When further preserved, products manufactured according to the invention are suitable as constructional elements, building parts and the like. These products are durable, light, mouldable, insulating and of sandwiched-shaped composition.
A product manufactured according to the invention is in general self-extinguishing, whereas comparable products manufactured from, for instance, (paper) pulp or EPS are relatively combustible. Moreover, the manufacture of such pulp products is labor-intensive and costly, the products are less strong, heavy, little resistant to, for instance, high temperatures and moisture, and the freedom of design is slight. A number of these and comparable drawbacks occur with comparable products manufactured from plastic, such as polystyrene foam and the like.
By controlling the process conditions, in particular the feed rate of the mass, the temperature of the mould and the pressure in the mould, a product is manufactured in which the cells are smaller adjacent the mould wall then centrally between the walls of the mould. In other words, in the product the cell size increases from the inside to the outside. Thus, a relatively closed, water-tight skin is obtained which properly protects the product from premature decline, while the inside of the product comprises relatively large cells which can keep the product light and flexible. Moreover, the foam-shaped inside is particularly favorable for obtaining and increasing the insulating action. A further advantage of the skin with a relative large density is that, as a result, a taut and smooth surface is obtained which affords the product an agreeable appearance, has a pleasant feel, is simply removable from the mould, is simply printable and moreover hygienic. Accordingly, in contrast with the known methods, a cell structure is obtained which is non-homogenous, at least viewed across the wall thicknesses.
The use of recycled fibers, for instance paper fibers or like cellulose fibers, offers the advantage that a relatively cheap and environmentally friendly basic material can be used. Such recycled fibers are relatively cheap and widely available. Moreover, a product obtained according to such method can, after use, be incorporated into the same waste flow and reused in such products.
By using fibers coming from annual plants, in particular by only using fibers which preferably come from annual plants and/or from recycling, the advantage is achieved that products can be manufactured in a particularly environmentally friendly manner. The use of fibers from annual plants is preferred to fibers from, for instance, trees, because these annual plants are quickly renewable, are relatively cheap and readily available. Moreover, the use of annual plants stimulates diversification in agriculture. In particular wood cutting is not necessary for this. Further, annual plants produce relatively long fibers. When used, these fibers have the advantage that the flexibility of the products obtained is considerably increased thereby. The fibers act as a kind of reinforcement.
By coating at least a portion of the fibers to be used in the method, water absorption by the fibers is limited to a minimum, at least to a favorable low value. This limits or prevents thickening of the mass, so that the processing thereof remains possible in an simple manner, also in the case of relatively long paths of flow. Moreover, the baking process is accelerated thereby, because less water needs to be evaporated, which is also favorable from an energetic viewpoint. Moreover, the coating enables in a particularly simple manner the addition of additives to the mass. The coating can for instance consist of means for obtaining a better bond between the fibers and, for instance, the starch from which the cells are blown. Moreover, the coating can contain for instance, a blowing agent, colorants, natural anti-fungal agents, flavorings and/or fragrances, and the like.
The addition of at least 0.5% and preferably between 2% and 25% fibers offers the advantages that the mass can be introduced into the mold in a relatively simple and suitable manner and results in a proper distribution thereof in the mold, while the above-mentioned advantages are achieved. In particular when 4-15% fibers is added, particularly favorable results are achieved.
The addition of 15-75% dry substance in the mass, and more advantageously between 20-60% dry substance yields advantageous results. In the starting condition, i.e. at a temperature below the gelatinization temperature, a mass thus designed has good flowing properties, while products having the above-mentioned favorable properties are obtained thereby. In particular when using a mass containing between 30-50% dry substance, particularly favorable results are achieved thereby.
The above-mentioned percentages are in each use mentioned for suspensions used, not for any prefoamed mass. The percentages present therein can easily be derived from these compositions.
By building up the products according to the invention from dish or sheet parts each having at least one slight thickness with regard to the other dimensions, at least with regard to outside dimensions, voluminous products can be manufactured which can yet be supplied at all points with so much heat during the preparation that the desired extent of cross-linkage occurs. Thus, dish-shaped products can be manufactured, that is, also block-shaped products, with, for instance, a recess in which a product to be packaged can be wholly or partly received, and filler blocks for, for instance, packages, can be manufactured. Also, for instance through extrusion, for instance hollow or finned profiles can be manufactured. A further advantage of the relatively thin sheet parts is that, as a result, a relatively great flexibility is obtained while the products yet maintain the desired strength properties and volumes.
By making use of a batter which is liquid below the gelatinization temperature, preferably at room temperature, supply of the batter can be realized in a simple manner, for instance via pipes and using simple pumping means. Moreover, a stock of the batter can be priorly prepared and be fed to a processing apparatus directly from a storage tank. In this connection, the liquidity of the batter provides the advantage that the flow paths in the mould can he particularly long. The water in the batter functions as blowing agent and moreover, upon evaporating from the mould, provides space for the expansion of the cells.
The batter preferably consists entirely of constituents coming from renewable sources, in particular in the form of a suspension. As a result, good flow properties of the batter are maintained and crude starting material such as starch can be used, for instance potato starch or tapioca. Moreover, such a suspension can be simply stored, at least better than a mixture already gelatinized.
Mentioned as suitable natural polymers are native starch, for instance potato starch, maize starch, wheat starch, waxy maize starch, tapioca starch, pea starch, high-amylose starch or rice starch. Preferably, however, potato starch is used with an amolypectin content of between 75 and 100%. Starch derivatives can also be used, for instance, starch which has been modified by etherification, esterification, acid hydrolysis, oxidation, cross-linking and/or the action of enzymes.
The use of relatively dry, optionally slightly prefoamed starting material provides the advantage that relatively little water or other moisture needs to evaporate in the mould, which has appreciable energetic advantages, the more so since the mass only needs to be heated in the mould, not in the pre-stage. The mass can for instance consist of granulate material, in particular more or less spherical particles having small to very small dimensions with respect to the passage openings to and in the mould. This granulate material can contain a blowing agent, for instance in the form of water or blowing agents simply released and/or evaporating upon heating, such as bicarbonates, which provides for gas evolution through decomposition at elevated temperature.
As starting materials, for instance, the natural polymers mentioned in respect of the batter can be used.
In a further advantageous embodiment, a method according to the invention is characterized in that as mould an injection mould is used.
By making use of an injection mould in a method according to the invention, products can be manufactured with both regular and irregular shapes, which are dimensionally stable and can have varying wall thicknesses. Products manufactured in this manner can, for instance, be used as sheet and dish parts, trays and boxes and like dish-shaped packages and as filler for, for instance, packaging products in boxes and the like, and as constructional or building part. One of the important advantages that can be achieved with this method is that a greater freedom in design is obtained than when platen sets are used. The products can be manufactured in withdrawable as well as non-withdrawable manner, since divisible cores and the like can be readily utilized. As a result, for instance undercuts can be integrally moulded. Moreover, greater differences in height can be incorporated in the product in that the flow path can be longer and gravity has no influence, at least no appreciable influence, on the distribution of the mass.
In a further advantageous embodiment, a method according to the invention is characterized in that an extension die is used.
When nursing an extrusion die in a method according to the invention, sections and the like can be manufactured in a simple manner with the above-mentioned advantages of the cross-linked structure of the natural polymers. Owing to the mass being supplied in cold, preferable liquid form, the preparation thereof is particularly simple and products with the desired properties can be manufactured in substantially one processing pass. In this manner, for instance, sheets and sections can be extruded which are used in great lengths or can be divided up and, for instance, be used as loose filler in the packaging of products in boxes, crates, bags, as decorative parts, as constructional element and as building part and the like. Extrusion and the use of an extrusion die should herein be understood to mean in particular forcing a moulding mass under pressure through a relatively small orifice, this orifice determining substantially at least one cross section of the product. The delivery pressure can, for instance, be generated with a pump or a plunger.
Products that are manufactured with a method according to the invention can in a general sense be designed light with respect to the volume, have sufficient strength and elasticity and are properly resistant to different conditions, in particular when using a xe2x80x9cskinxe2x80x9d with a relatively high density and a core with a relatively low density.
During the manufacture of the products according to the invention, gas formation through evaporation of water or under the influence of blowing agents occurs so fast that foaming occurs concurrently with or preferable prior to the gelatinization. At elevated pressure and/or temperature this effect is achieved, while further more solid material is xe2x80x9ccompressedxe2x80x9d as cell wall. This not only yields a core made up of a large cells with firm cell walls but also skin layers with a higher degree of densification of firm small cells.
In addition, there may be a number of other conditions that must be met to obtain the desired result.
The colloidal particles and corresponding conditions must meet requirements to provide for the formation of foam, which requires, among other things, a particular load and particular surface tensions, in conjunction with an internal and external pressure in the foam bubbles.
The charging of the mould cavity must be complete within a very short time, which entails requirements for the xe2x80x9cflowxe2x80x9d properties and the thrust: during this short period the xe2x80x9cflowxe2x80x9d properties must remain sufficient to ensure complete filling, while the driving force, the propellant or xe2x80x9cfoamxe2x80x9d gas, must remain present in a sufficient amount to advance the mass (which is increasingly hard to move). Flow should herein be understood to include both the flow of a liquid, such as the liquid batter, and the flow of a granulate-form, relatively dry substance such as small rolling and sliding granules or powder, whether or not in slightly prefoamed form.
Accordingly, the length of the flow path is at least dependent on the liquidity of the starting material and, given equal conditions, will be greater for a liquid or suspension than for granulate material. Moreover, the length of the flow path will be positively influenced by a greater difference between the low supply temperature and the temperature of the mould during the baking. Surprisingly, it has been found that when fibers, in particular natural fibers, are added to a mass for use in a method according to the invention, the flow properties are not, or only to a very slight extent, adversely affected, particularly in the case of relatively short to medium-length fibers. Fibers to be used will on average have a length of between 0.5 and 10 mm, maximally a length of about 130 mm, and average diameters between 1 and 100 xcexcm. The fibers can be branched as well as unbranched, open or still closed, while they may contain lignin and may comprise fiber fibrils. Short fibers have a length of less than 1 mm, long fibers have a length of more than 4 mm, medium-length fibers have a length of between 1 and 4 mm. Thus, if so desired, the fiber distribution in the mold, and accordingly in each product manufactured, can be uniformly obtained, so that the product properties are regularly obtained.
The invention further relates to apparatuses suitable for use in a method according to the invention.
Such a package has the advantage that it can be considered a so-called mono-material package, so that the package can as a whole be incorporated into the same water flow, in particular a paper, cardboard and recycling flow. To manufacturers as well as users, this has the advantage of involving only a slight environmental burden, while the user does not have to separate the package and present it separately, while the manufacturer is not forced to take back the separated package parts and/or does not have to pay a relatively high compensation for the eventual processing of the package. The fibers in the product, manufactured according to the invention, offer the advantage of having a paper-like or cardboard-like appearance, so that it will be directly clear to the consumer that this package can be incorporated into a paper-waste flow. Moreover, in view of the filling of the mold, indications such as names and recycling symbols can readily be included, in relief, in the product. Owing to the dense skin, it can be printed in an excellent manner.
Further advantageous embodiments of methods, apparatuses and products according to the invention are presented in the subclaims.
The invention moreover relates to products manufactured with a method and/or in an apparatus according to the invention.
Products manufactured according to the invention can be considered to be paper-like products.